Two phase detonation studies

An experimental study of the passage of a shock wave over a burning fuel drop is described. This includes high speed framing photographs of the interaction taken at 500,000 frames per second. A theoretical prediction of the ignition of a fuel drop by a shock wave is presented and the results compared with earlier experimental work. Experimental attempts to generate a detonation in a liquid fuel drop (kerosene)-liquid oxidizer drop (hydrogen peroxide)-inert gas-environment are described. An appendix is included which gives the analytical prediction of power requirements for the drop generator to produce certain size drops at a certain mass rate. A bibliography is also included which lists all of the publications resulting from this research grant

Theoretical analysis of magnetic coupling in sandwich clusters V_n(C_6H_6)_{n+1}

The mechanism of ferromagnetism stability in sandwich clusters V$_n$(C$_6$H$_6$)$_{n+1}$ has been studied by first-principles calculation and model analysis. It is found that each of the three types of bonds between V and benzene (Bz) plays different roles. V 3d$_{z^2}$ orbital, extending along the molecular axis, is weakly hybridized with Bz's HOMO-1 orbital to form the $\sigma$-bond. It is quite localized and singly occupied, which contributes 1$\mu_B$ to the magnetic moment but little to the magnetic coupling of neighboring V magnetic moments. The in-plane d$_{x^2-y^2}$, d$_{xy}$ orbitals are hybridized with the LUMO of Bz and constitute the $\delta$-bond. This hybridization is medium and crucial to the magnetic coupling though the $\delta$ states have no net contribution to the total magnetic moment. d$_{xz}$, d$_{yz}$ and HOMO of Bz form a quite strong $\pi$-bond to hold the molecular structure but they are inactive in magnetism because their energy levels are far away from the Fermi level. Based on the results of first-principles calculation, we point out that the ferromagnetism stability is closely related with the mechanism proposed by Kanamori and Terakura [J. Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the presence of edge Bz's in the cluster introduces an important modification. A simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure

Effect of ionic strength on complexation of Pu(IV) with humic acid

International audienceSuccessful geochemical modelling of the migration of radioactive materials, such as the transuranic elements, from nuclear waste repositories is dependent upon an understanding of their interaction with biogeopolymers such as humic acids, the most likely complexing agents in groundwaters. An established silica/humic acid composite has been evaluated as a model substrate for naturally occurring humate-coated minerals that are likely to be present in the vicinity of the repositories. The binding of Pu(IV), the highly likely oxidation station, by the silica/humic substrate was examined at pH 4 in the range 0.02 to 3.00M NaClO$_4$ by the titration method. Pu(IV)-humate conditional stability constants have been evaluated from data obtained from these experiments by using non-linear regression of binding isotherms. The results have been interpreted in terms of complexes of 1:1 stoichiometry. Analysis of the complex formation dependency with ionic strength shows that the effect of ionic strength on humate complexation of Pu(IV) is not dramatically pronounced. The complexation constants are evaluated for the humate interaction with Pu$^{4+}$ and Pu(OH)$_3^+$ at pH 4. The complexation constants are found, respectively, to be log$^{HA}$$\beta ^0$(Pu$^{4+}$)=16.6$\pm$0.3 and log$\beta ^0_{1.3.1}$=46.6$\pm$2.3. The estimations through analogy from previous results are in agreement with these new experimental data

Contactless electrical conductivity measurement of metallic submicron-grain material: Application to the study of aluminum with severe plastic deformation

We measured the electrical conductivity σ of aluminum specimen consisting of submicron-grains by observing the AC magnetic susceptibility resulting from the eddy current. By using a commercial platform for magnetic measurement, contactless measurement of the relative electrical conductivity σn of a nonmagnetic metal is possible over a wide temperature (T) range. By referring to σ at room temperature, obtained by the four-terminal method, σn(T) was transformed into σ(T). This approach is useful for cylinder specimens, in which the estimation of the radius and/or volume is difficult. An experiment in which aluminum underwent accumulative roll bonding, which is a severe plastic deformation process, validated this method of evaluating σ as a function of the fraction of high-angle grain boundaries

Rectification of radio frequency current in ferromagnetic nanowire

We report the rectification of a constant wave radio frequency (RF) current by using a single-layer magnetic nanowire; a direct-current voltage is resonantly generated when the RF current flows through the nanowire. The mechanism of the rectification is discussed in terms of the spin torque diode effect reported for magnetic tunnel junction devices and the rectification is shown to be direct attributable to resonant spin wave excitation by the RF current.Comment: 20 Pages, 4 figures, submitte

Emission of radon and thoron due to the fracture of rock

In order to investigate the fundamental processes of radon anomaly related to earthquakes, the measurement of the emission of radon and/or thoron from a rock under pressure has been carried out. The thoron emission increases after the crush of a rock. Before the crush, however, its increase is scarcely observed during compression. The emission of thoron varies under the gradual compression of the lumps of fractured rocks and diminishes to zero when they are compressed entirely. It is suggested from these facts that the precursory anomaly of radon related to earthquakes occurs in the fractured rock region such as faults

The effect of potassium on aluminous phase stability in the lower mantle

The aluminous calcium-ferrite type phase (CF) and new aluminous phase (NAL) are thought to hold the excess alumina produced by the decomposition of garnet in MORB compositions in the lower mantle. The respective stabilities of CF and NAL in the nepheline-spinel binary (NaAlSiO4 –MgAl2O4 ) are well established. However with the addition of further components the phase relations at lower mantle conditions remain unclear. Here we investigate a range of compositions around the nepheline apex of the nepheline-kalsilite-spinel compositional join (NaAlSiO4 –KAlSiO4–MgAl2O4 ) at 28–78 GPa and 2000 K. Our experiments indicate that even small amounts of a kalsilite (KAlSiO4 ) component dramatically impact phase relations. We find NAL to be stable up to at least 71 GPa in potassium-bearing compositions. This demonstrates the stabilizing effect of potassium on NAL, because NAL is not observed at pressures above 48 GPa on the nepheline-spinel binary. We also observe a broadening of the CF stability field to incorporate larger amounts of potassium with increasing pressure. For pressures below 50 GPa only minor amounts (<0.011(1) K/(K+Na+Mg) ) of potassium are soluble in CF, whereas at 68 GPa, we find a solubility in CF of at least 0.088(3) K/(K+Na+Mg). This indicates that CF and NAL are suitable hosts of the alkali content of MORB compositions at lower mantle conditions. For sedimentary compositions at lower mantle pressures, we expect K-Hollandite to be stable in addition to CF and NAL for pressures of 28–48 GPa, based on our simplified compositions

Theory of optical spectra of polar quantum wells: Temperature effects

Theoretical and numerical calculations of the optical absorption spectra of excitons interacting with longitudinal-optical phonons in quasi-2D polar semiconductors are presented. In II-VI semiconductor quantum wells, exciton binding energy can be tuned on- and off-resonance with the longitudinal-optical phonon energy by varying the quantum well width. A comprehensive picture of this tunning effect on the temperature-dependent exciton absorption spectrum is derived, using the exciton Green's function formalism at finite temperature. The effective exciton-phonon interaction is included in the Bethe-Salpeter equation. Numerical results are illustrated for ZnSe-based quantum wells. At low temperatures, both a single exciton peak as well as a continuum resonance state are found in the optical absorption spectra. By contrast, at high enough temperatures, a splitting of the exciton line due to the real phonon absorption processes is predicted. Possible previous experimental observations of this splitting are discussed.Comment: 10 pages, 9 figures, to appear in Phys. Rev. B. Permanent address: [email protected]

Absorption of Scintillation Light in a 100 ℓ\ell Liquid Xenonγ\gamma Ray Detector and Expected Detector Performance

An 800L liquid xenon scintillation $\gamma$ ray detector is being developed for the MEG experiment which will search for $\mu^+\to\mathrm{e}^+\gamma$ decay at the Paul Scherrer Institut. Absorption of scintillation light of xenon by impurities might possibly limit the performance of such a detector. We used a 100L prototype with an active volume of 372x372x496 mm$^3$ to study the scintillation light absorption. We have developed a method to evaluate the light absorption, separately from elastic scattering of light, by measuring cosmic rays and $\alpha$ sources. By using a suitable purification technique, an absorption length longer than 100 cm has been achieved. The effects of the light absorption on the energy resolution are estimated by Monte Carlo simulation.Comment: 18 pages, 10 figures (eps). Submitted to Nucl. Instr. and Meth.

Amorphization and decomposition of scandium molybdate at high pressure

The behavior of negative thermal-expansion material scandium molybdate Sc2(MoO4)3 is investigated at high pressure (HP) and high temperature (HT) using x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The compound exhibits unusually high compressibility (bulk modulus ~6 GPa) and undergoes amorphization at 12 GPa. On the other hand, in situ laser heating of amorphous samples inside the diamond-anvil cell is found to result in crystalline diffraction pattern and Raman spectrum different from those of the original compound. Upon release of the pressure subsequent to laser heating, the Raman spectrum and the diffraction pattern remain unchanged. Matching of several of the diffraction lines and Raman peaks in the laser-heated samples with those of MoO3 suggests a solid-state decomposition of the parent compound under HP-HT conditions into MoO3 and other compounds. Other diffraction lines are found to correspond to Sc2Mo2O9, Sc2O3, and the parent compound. Quantitative analysis of the characteristic x-ray emission from different regions of the sample during scanning electron microscopic observations is used for obtaining the compositions of the daughter compounds. The stoichiometries of two main phases are found to be close to those of MoO3 and Sc2Mo2O9. These results support the model that the pressure-induced amorphization occurred in this system because a pressure-induced decomposition was kinetically constrained